1. Field of the Invention
The present invention relates to an envelope capable of keeping its interior hermetically sealed and a method of manufacturing the same. The envelope is suitable for an image-forming apparatus.
2. Related Background Art
Up to now, there have been known two types of electron-emitting devices, a thermionic source and a cold cathode electron source. The cold cathode electron source includes a field emission device (hereinbelow referred to FE device), a metal/insulating-layer/metal device (hereinbelow referred to MIM device), and a surface conduction electron-emitting device (hereinbelow referred to SCE device).
Concerning those technologies, some examples of background arts proposed by the present inventor are as follows. Device formation using an inkjet formation method is described in detail in Japanese Patent Application Laid-open No. 09-102271 and Japanese Patent Application Laid-open No. 2000-251665. An example in which those devices are arranged in an XY-matrix shape is described in detail in Japanese Patent Application Laid-open No. 64-031332 and Japanese Patent Application Laid-open No. 07-326311. Further, a wiring forming method is described in detail in Japanese Patent Application Laid-open No. 08-185818 and Japanese Patent Application Laid-open No. 09-050757. A driving method is described in detail in Japanese Patent Application Laid-open No. 06-342636 and the like.
Up to now, seal bonding has been employed in manufacturing an envelope which keeps its interior vacuum. In the seal bonding, frit glass as a seal member is applied or placed between glass members, and then the entire envelope is put into a seal bonding furnace such as an electric furnace, or put on a hot plate heater (or interposed between an upper hot plate and a lower hot plate), and heated to a seal bonding temperature to melt and bond the seal bonding portions of the glass members with the seal bonding glass. An example of such an envelope manufacturing method is disclosed in Japanese Patent Application Laid-open No. 11-135018.
Japanese Patent Application Laid-open No. 2001-210258 discloses a flat panel display in which a low melting point metal is used for seal bonding. Japanese Patent Application Laid-open No. 2001-210258 also discloses use of a material that has high affinity to a low melting point metal material formed on a seal bonding surface as a measure of holding the low melting point metal material.
Flat panel displays using electron sources need ultra high vacuum in order to operate cold cathode electron-emitting devices and the like stably for a long period of time. Therefore, in such flat panel displays, a substrate having plural electron-emitting devices and a substrate having phosphors which face each other across a frame are seal-bonded to each other with frit glass and a getter is provided to maintain the vacuum state by adsorbing discharged gas.
Getters are classified into evaporables and non-evaporables. Evaporating getters are alloys each mainly containing Ba or the like. An evaporating getter is heated in a vacuum glass envelope by energization or high frequency to form an evaporation film on an inner wall of the container (getter flash), and gas generated in the container is adsorbed by an active getter metal face to maintain high vacuum.
On the other hand, non-evaporating getters are Ti, Zr, V, Al, Fe, and the like. A non-evaporating getter material is heated in vacuum for “getter activation”, which gives the getter material a gas adsorbing characteristic. The getter material thus can adsorb discharged gas.
Flat panel displays in general are thin and have difficulties in finding enough space to set an evaporating getter which maintains vacuum and to provide a flash region for instant electric discharge. Accordingly, the getter setting region and the flash region are placed near a supporting frame outside the image display area. This reduces conductance between a central portion of the image display area and the getter setting region, and slows the effective exhaust speed of the electron-emitting devices and the phosphors at the central portion. In an image display device having an electron source and an image display member, the major area where produces undesirable gas is generated is the image display region which is irradiated with an electron beam. Accordingly, a non-evaporating getter has to be placed in the vicinity of phosphors and the electron source which are the sources of undesirable gas if the phosphors and the electron source are to be kept in high vacuum.